1. Field of the Invention
The present invention relates a mechanical scan type ultrasonic probe for performing mechanical scanning of an ultrasonic beam with respect to an object to be examined.
2. Description of the Related Art
A conventional mechanical scan type ultrasonic probe of this type will be described below with reference to FIG. 1. FIG. 1 is a sectional view showing a body cavity mechanical scan type ultrasonic probe used for diagnosis of the interior of a body cavity, e.g., the gullet, the intestines, a blood vessel, and the like in an object to be examined. This probe is disclosed in Published Examined Japanese Patent Application No. 63-34737.
As shown in FIG. 1, the rotational force of a motor 100 as a rotating means is transmitted to a rotating shaft 106 through gears 102 and 104. This rotational force is transmitted from the rotating shaft 106 to a rotor 110 through a rotational force transmitting shaft 108 constituted by a multiple spiral spring. Since the rotational force transmitting shaft 108 is constituted by the multiple spiral spring, it has both flexibility and expandability and can efficiently transmit a rotational force. The rotational force transmitting shaft 108 shown in FIG. 1 is constituted by a double spiral spring as an example. The rotor 110 is arranged in the internal space of an inserting portion 10 to be inserted in a body cavity (not shown). An ultrasonic transducer 112 is arranged on an end portion of the rotor 110. With this arrangement, the ultrasonic transducer 112 is rotated integrally with the rotor 110. One end of each of a pair of signal lines 114a and 114b is connected to a corresponding one of rotating terminals 116a and 116b, which are rotated integrally with the rotating shaft 106, through a hollow portion 108a of the rotational force transmitting shaft 108. The other end of each of the pair of signal lines 116a and 116b is connected to the transducer 112. With this arrangement, the pair of signal lines 116a and 116b are also rotated integrally with the transducer 112. In this arrangement, supply of a driving signal to the transducer 112 and extraction of an echo signal received by the transducer 112 are performed by a slip ring mechanism constituted by the rotating terminals 116a and 116b and fixed terminals 118a and 118b.
The rotational force transmitting shaft 108 constituted by the double spiral spring is guided into a pipelike guide 120 to retain its shape. In some cases, however, the rotational force transmitting shaft 108 cannot exhibit sufficient expandability because of friction with the pipe-like guide 120 depending on how the shaft 108 is bent. As a result, the rotor 110 may not be smoothly rotated.
In order to eliminate such a drawback, the pipelike guide 120 or the rotational force transmitting shaft 108 is designed to be axially slidable. This arrangement is disclosed in Published Unexamined Japanese patent Application No. 61-64240. FIG. 2 shows an example of the above-mentioned arrangement, in which a metal fitting 124 having a flange 122 is connected to the distal end portion of a pipe-like guide 120. In addition, a cylindrical space portion 126 corresponding to the flange 122 is formed in an inserting portion 10 to constitute a slide mechanism. The metal fitting 124 is designed to be moved in a direction indicated by an arrow together with the flange 122 so as to allow the pipe-like guide 120 to freely slide in the axial direction.
In order to realize such a conventional arrangement, a complicated slide mechanism including a bearing is required. In addition, the pipe-like guide 120 may be distorted even when the rotational force transmitting shaft 108 is slightly bent. As a result, the friction between the rotational force transmitting shaft 108 and the pipe-like guide 120 is increased, and hence smooth transmission of a rotational force to the rotor 110 becomes difficult.
Furthermore, in the conventional mechanical scan type ultrasonic probe when the transducer 112 (rotor 110) is rotated at high speed, disconnection of the signal lines 114a and 114b tends to occur. More specifically, if the transducer 112 (rotor 110) is rotated at high speed while the rotational force transmitting shaft 108 constituted by the double spiral spring is bent, since a tension acts on the rotational force transmitting shaft 108, the signal lines 114a and 114b may be disconnected. In addition, since the rotational force transmitting shaft 108 is constituted by a spring, the signal lines 114a and 114b may be caught in the gap between turns of the spring and tend to be disconnected upon bending of the shaft 108 or by the friction between the shaft 108 and the pipe-like guide 120. Moreover, since the diameter of the hollow portion 108a of the rotational force transmitting shaft 108 is 1 mm at best, a cumbersome operation is required to insert the signal lines 114a and 114b into the space of the hollow portion 108a to a depth of 1 mm or more.